(a) Field of the Invention
The present invention relates to a high tenacity industrial polyester fiber and a method of preparing the same, and more particularly to an industrial high tenacity polyester fiber with a superior creep property and that can have various industrial uses including as a tire cord for reinforcing rubber, and for a seat belt, a conveyor belt, a V-belt, a rope, a hose, and the like, and a method of preparing the same.
(b) Description of the Related Art
In order to prepare a fiber, a high tenacity fiber is generally prepared by changing various process parameters, such as a spinning temperature, a quench air temperature, a temperature of godet rollers and a velocity ratio thereof, and the like. Particularly, a method of minimizing orientation of an undrawn fiber before drawing process is used in the preparing process of an industrial polyester fiber so as to reveal the properties in the fiber-making processes (synthesis of raw materials, polymerization, and spinning).
However, there is a limitation of applying the fiber to a real manufacturing process, because it is difficult to reveal the properties and the quality and the processibility thereof deteriorate when the orientation of the undrawn fiber increases.
This is caused by the characteristics of the polyester polymer itself, and a conventional polyester fiber shows a tenacity property of 9.3 g/d or less. Therefore, developments for optimizing properties while equally maintaining the quality and processibility of the industrial polyester fiber are ongoing.
As an example, U.S. Pat. No. 4,690,866 suggested a spinning method using polyester chips having a high intrinsic viscosity (IV) of 1.2 or more as a method for increasing the tenacity of a polyester multi-filament fiber. In this way, when the intrinsic viscosity of the chips is raised, the spinning tension increases and the orientation uniformity of the undrawn fiber and the formation of tie-chains connecting crystals increase, and thus it can show superior tenacity when the fiber is made into a final product. However, the polyester having high intrinsic viscosity used in the method has a large difference in intrinsic viscosities between the surface and the core when it is made by solid-state polymerization. When melt-spinning it, therefore, the spinnability deteriorates due to the heterogeneity of the viscosity, and the processibility and the appearance become inferior because of hairiness generated at the filaments. Furthermore, there is also a problem in that thermal degradation and hydrolysis are generated, and the spun fiber cannot actually have as much intrinsic viscosity as the chips have because it must be melt-spun at a high temperature.
Furthermore, when preparing the polyester fiber by using a usual spinning device, there are limitations in the qualities of fiber and the processibility for exhibiting the high tenacity of 9.5 g/d or more. Thus far, properties surpassing the target value (9.0 g/d) can be obtained by minimizing the orientation differences of undrawn fiber, but there is a difficulty in exhibiting properties beyond that because of the characteristics of the polymer.